Generally, in windmills for wind power generation, there are known a horizontal shaft type windmill in which a rotating shaft thereof is made to be horizontal relative to wind as represented by a dutch type windmill and a vertical shaft type windmill in which a rotating shaft thereof is made to be orthogonal relative to wind.
Among them, in vertical shaft type windmills, there are known a drag type windmill in which a windmill is rotated by a drag generated at a blade thereof as in a paddle type, Sabonius type or the like and a lift type in which a windmill is rotated by a lift generated at a blade thereof as in Darrieus type, a gyro mill type or the like. That is, whereas the former rotates the windmill by a drag difference by reducing resistance of the blade directed to the windward, the latter rotates the windmill by the lift generated at the blade (for example, refer to Patent Literature 1 discussed below).
[Patent Literature 1]
JP-A-54-153944
However, in the case of the former of the vertical shaft type (drag type), there poses a problem that when a peripheral speed ratio (blade end speed/wind speed becomes 1, a moment for rotating the windmill more than the peripheral speed ratio is not generated, even when the wind speed is increased, a rotational number more than the wind speed cannot be achieved and a power generation efficiency is poor. Meanwhile, in the case of the latter (lift type), when the peripheral speed ratio is equal to or lager then 1, than aerodynamic property of the windmill is improved and the windmill can be rotated efficiently. However, when the peripheral speed is smaller than 1, the aerodynamic property of the windmill is deteriorated and the moment for rotating the windmill is reduced. Further, there is a drawback that a starting moment is small and starting from a stationary state becomes very difficult.
Hence, there is known, for example, the device shown in Patent Literature 2 (JP-A-2001-132615) or the like which increases the power generation efficiency by improving the shape of the blade. The publication discloses a windmill of the propeller type (lift type) of a horizontal shaft type, as shown by FIG. 7, there is disclosed a constitution in which a plurality of windmill blades 53 are provided at constant angles from a rotating shaft 51 via a rotor 52 in a face orthogonal to the rotating shaft 51, wherein the insides of the respective windmill blades 53 are provided with auxiliary blades 54 included therein extractably and retractably to and from respective front ends thereof, at a low wind speed region, the auxiliary blade 54 is projected from a position designated by two-dotted chain lines at inside of the windmill blade 53 to an upper side of FIG. 7 in an arrow mark direction of FIG. 7 and the rotational torque is increased by increasing the lift.
However, the windmill is a windmill of a horizontal shaft type and there poses a problem that even when the power generation efficiency is increased, a number of parts is increased and the cost is increased. Therefore, there is a drawback that the cost of the apparatus is increased in order to achieve the same power generation function.
Incidentally, as shown by FIG. 8, Patent Literature 1 discloses a vertical shaft type windmill in which a rotor shaft 61 is attached with a blade fixing plate 62 and a bent blade 63 is attached to the rotor shaft 61 by an angle of elevation of 0 degrees relative to a rotor shaft 61 between the blade fixing plates 62. However, according to Patent Literature 1, only an example of bending the blade 63 is shown and a specific structure of the blade 63 is not disclosed at all.